Study On Geological Characteristics,Geochemical Characteristics And Metallogenic Model Of Yaojialing Zn-Au Polymetallic Deposit In Tongling,Anhui Province

The Yaojialing polymetallic Zn-Au deposit is a typical deposit in the Tongling ore district of the Middle-Lower Yangtze River metallogenic belt,it is composed of three mineralization-alteration types,including porphyry-type,skarn-type and vein-type.The main ore body is mostly located in the xenoliths and their contact zones in intrusive rocks,The unique output elements and occurrence locations of the ore body has great research significance in the Tongling ore district,which is dominated by developed layered skarn copper-gold deposits.On the basis of previous studies,a detailed mineralogical,geochemical and fluid inclusion geochemistry has been carried out on the Ore-bearing rock mass and different types of ore in Yaojialing deposit.This paper this paper identify the geological characteristics,Ore-forming mechanism,Ore-controlling factors and genesis of ore deposits,the following main understandings has been obtained.1.Thought of the study of the main,trace elements and rare earth elements in Yaojialing rock,it indicates that the ore-forming granodiorite porphyry belongs to metaluminous high-K calcium alkaline " ? " type granite,its age is defined to be138.6±2.9Ma by using LA-ICP-MS zircon U-Pb dating,suggesting that the rock belonged to the product of localization of mid-acid magma in the late Yanshan Early Cretaceous.Through the analysis of magma source,formation environment and formation process,The Yaojialing rock originated from the enriched mantle,formed in the inland environment of the magmatic arc on the active continental margin,and intruded into the lower crust during the transition from collision to extension to form crust-mantle mixed source magma.After undergoing crystallization differentiation and assimilation and contamination with the crust material in the middle and shallow parts,the high-calcium-calcium alkaline intrusive rock in this area was finally formed.2.Through the study of the ore body characteristics,ore characteristics and wall rock alteration of the deposit,it is found that the porphyry-type ore body mostly develops copper and gold mineralization,which is mainly deposited in the mid-deep granodiorite porphyry body;the skarn-type and vein-type ore body mostly develop lead-zinc mineralized and they are deposited in the upper and lower contact zones and interlayer fissures in marble of the middle and shallow parts.The ores of the three types of ore bodies have veins,intrusions,and massive structures.According to the symbiotic combination and interpenetration of minerals,This article divides themetallogenic stage into four stages: early skarn stage,mid-stage oxide stage,main metallogenic stage quartz-sulfide stage and late carbonate stage.3.The Yaojialing granodiorite porphyry intruded into the body with a tubular Cryptoexplosive breccia body,which fell vertically to the northwest side,and the most of ore bodies are distributed in the Cryptoexplosive breccia tube.According to the formation mechanism and environment of cryptoexplosive breccia,Yaojialing cryptoexplosive breccia can be roughly divided into the middle and lower part of Cryptoexplosive magmatic clastic breccia,the middle and upper part of cryptoexplosive hydrothermal breccia and the edge part of cryptoexplosive rupture rock.According to the obvious vertical zoning of the hidden explosion breccia tube,it is divided into the fissure phase at the top,the blasting phase at the middle and upper parts,the shattering phase at the middle and lower parts,and the shocking phase at the bottom.This reveals the formation mechanism of the hidden explosion breccia tube,ore-forming metal elements are mostly concentrated and precipitated in deep and edge parts to form various ore bodies.4.Analysis of trace element geochemistry of zircon and apatite accessory minerals in the ore-forming parent rocks reveals that zircon has obvious Ce positive anomalies(?Ce=5.54?69.3,average 19.8)and Eu negative anomalies(?Eu=0.38?0.80,average 0.60),apatite has a medium negative Eu anomaly(?Eu average 0.63)and basically no Ce anomaly(?Ce average 1.04),these indicate that the parent magma is formed in an oxidizing environment,which is beneficial to ore-forming metal The final enrichment and precipitation in the rock mass.5.Geochemical studies of fluid inclusions indicate that the ore-forming fluid has experienced a continuous evolution process that from high temperature,medium salinity,low density to low temperature,low salinity,and medium-low density,which basically corresponds to various stages of the metallogenic process.The H-O isotope composition indicates that the ore-forming fluids in the early ore-forming period are mainly magmatic water,which is closely related to the formation of porphyry-type ore body,later mixed with a small amount of atmospheric precipitation,which is beneficial to the formation of skarn-type ore body and vein-type ore body.The lowering of the temperature of ore-forming fluids and the mixing of fluids are the main factors leading to the precipitation of ore-forming metal elements.6.This paper summarizes the relationship between the main ore controlling factors such as strata,structure,magmatic rock and mineralization,discusses thegenesis of yaojialing Zn-Au polymetallic deposit and establishes the metallogenic model.The strong magmatic activity in the late Yanshanian period provided the main ore-forming materials,ore-forming fluids and heat sources for the formation of the Yaojialing deposit;the Carboniferous Huanglong-Chuanshan Formation and Permian Qixia Formation were also involved in mineralization;two sets of secondary fractures,the inverted Daigongshan anticline,interlayer slippage in limestone captivity and contact zone in the limestone captivity play an important role in controlling the positioning of the ore body.In summary,the Yaojialing Zn-Au polymetallic deposit is a Porphyry-skarn-shallow low temperature hydrothermal vein type deposits that formed in different structural parts of the same magmatic hydrothermal mineralization system.It controlled by formation lithology,magmatic activity and various structures.